title: Cap snatching in yeast L-BC double-stranded RNA totivirus.
abstract: Yeast L-A double-stranded RNA virus furnishes its transcript with a 5' cap structure by a novel cap-snatching mechanism in which m(7)Gp from a host mRNA cap structure is transferred to the 5'-diphosphate terminus of the viral transcript. His-154 of the coat protein Gag forms an m(7)Gp adduct, and the H154R mutation abolishes both m(7)Gp adduct formation and cap snatching. Here we show that L-BC, another totivirus closely related to L-A, also synthesizes 5'-diphosphorylated transcripts and transfers m(7)Gp from mRNA to the 5' termini of the transcripts. L-BC Gag also covalently binds to the cap structure and the mutation H156R, which corresponds to H154R of L-A Gag, abolishes cap adduct formation. Cap snatching of the L-BC virus is very similar to that of L-A; N7 methylation of the mRNA cap is essential for cap donor activity, and only 5'-diphosphorylated RNA is used as cap acceptor. L-BC cap snatching is also activated by viral transcription. Furthermore, both viruses require Mg(2+) and Mn(2+) for cap snatching. These cations are not only required for transcription activation but also directly involved in the cap transfer process. These findings support our previous proposal that the cap-snatching mechanism of the L-A virus is shared by fungal totiviruses closely related to L-A. Interestingly, L-A and L-BC viruses accept either viral transcript as cap acceptor in vitro. Because L-A and L-BC viruses cohabit in many yeast strains, it raises the possibility that their cohabitation in the same host may be beneficial for their mutual cap acquisition.
authors.affiliation: Instituto de Biología Funcional y Genómica, Consejo Superior de Investigaciones Científicas (CSIC)/Universidad de Salamanca, Salamanca 37007, Spain. tfujimura@usal.es
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Fujimura
authors.forename: Rosa
authors.initials: R
authors.lastname: Esteban
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002413:Cations, Divalent / Q000494:pharmacology; D011756:Diphosphates / Q000378:metabolism; D015683:Gene Products, gag / Q000737:chemistry / Q000378:metabolism; D006639:Histidine / Q000378:metabolism; D008969:Molecular Sequence Data; D010641:Phenotype; D012315:RNA Caps / Q000378:metabolism*; D012330:RNA, Double-Stranded / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012367:RNA, Viral / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000821:virology*; D019197:Totivirus / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D011756:Diphosphates; D015683:Gene Products, gag; D012315:RNA Caps; D012330:RNA, Double-Stranded; D012333:RNA, Messenger; D012367:RNA, Viral; D006639:Histidine
keywords: Cap Snatching; Capping; Double-stranded RNA; Gag; RNA Polymerase; RNA viruses; Transcription; Yeast; mRNA